Brian Krebs is perhaps uniquely qualified to write such a book, as he has long been intimately involved with the field, has a history of painstaking research, and has undoubted talents as a writer.
I also have an immediate selfish interest in hoping that this book is book is as good (and successful) as I hope it to be. Several of his posts are go-to answers to important questions. The Scrap Value of a Hacked PC, Revisited is good example. I don't have to write a careful response to questions of this nature, because Krebs has been there and done that--far better than I could. I can just send a link.
Here's the thing. Pre-orders are important in establishing the size of a print run. Writing any sort of book is an immense amount of work, which can be essentially wasted in terms of ROI if the books aren't available. Ebooks may mitigate this to some extent, but from what I've read, sales of physical books still matters a lot.
So, ROI. If his track record is any guide, the Investment has been very large. I'd like his Return to be large as well. You can think of this as a non-immediate selfish goal if, you like. Brian Krebs is a very effective Good Guy, and keeping him in the fight is a useful thing to do.